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Week 9 correlation

# Week 9 correlation - 1 SAN JOS STATE UNIVERSITY College of...

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1 SAN JOSÉ STATE UNIVERSITY College of Social Work S. W. 242 Spring 2009 Edward Cohen Week 9 March 20, 2009 Statistics review Correlation—Pearson r Lab 2b Independent t -test Final Paper discussion—Choosing a statistical procedure Next week: Happy Spring Break! Concepts you should know: Review univariate, bivariate, and multivariate analysis Correlation, or Pearson r , or Product-moment coefficient Assumptions of Pearson r Positive correlation Negative correlation I. Review A. Univariate, bivariate, or multi-variate analysis implied here? 1. The average age in your sample is 38, with a standard deviation of 12.82 2. Chi square test of association between gender and political party affiliation 3. Effects of group therapy (vs. individual therapy) on increasing score on a ratio level social support scale 4. Effects of group therapy (vs. individual therapy) on increasing score on ratio level social support scale, controlling for gender, ethnicity and SES B. Name that statistic:

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2 If … Independent variable is: And dependent variable is: Statistical test is: Categorical (nominal or ordinal) Categorical (nominal or ordinal) __________? Categorical (nominal— dichotomous, two independent groups) Ratio or interval __________? Categorical (two dependent groups) Ratio or interval __________? Categorical (nominal or ordinal) more than two attributes Ratio or interval __________? New! Continuous Continuous Correlation (Pearson r ) II. What is correlation? A. Correlation tests the relationship between a continuous independent variable and a continuous dependent variable. B. Examples of research scenarios: 1. The number of outpatient therapy sessions utilized is positively correlated with improvement in depression as measured by the total score of the Beck Depression Inventory 2. The number of hours students spend preparing for the 242 exam is positively correlated with the test score 3. The number of disruptive behaviors by children in residential care is negatively correlated with the number of strength-based supportive comments from staff C. Compare to other statistical tests: 1. Chi-Square: “The variables are associated…” 2. t -test: “The group means differ…” 3. ANOVA: “The group means differ…” 4. Correlation: “There is a positive [or negative] correlation between the two variables.” 5. (Preview to next class) Multivariate regression: “The independent variables ___, ___, ___, and ___ are related or predictive of the dependent variable ___, controlling for ____. D. Calculation of the Pearson r